The Science of Intermittent Hypoxic Exposure

Use of Intermittent Hypoxic Exposure (IHE) is relatively new in the west, but the USSR (and later CIS) has been researching and using IHE since the 1930's. Usage includes sports, altitude acclimatization, and treatment of clinical disorders, including chronic lung diseases, bronchial asthma, hypertension, diabetes mellitus, Parkinson's disease, emotional disorders, and even radiation toxicity.

1 Mechanisms

There appear to be three mechanisms underlying the effects of IHE: regulation of respiration, mitochondrial respiration, and free-radical production.

The regulation of respiration results in increased sensitivity of breathing rate to altitude, improved gas exchange in the lungs and changes to the autonomic nervous system.

Improvements in mitochondrial respiration results in optimized use of oxygen in energy production.

Exposure to both low and normal oxygen levels improves the body's antioxidant defense.

The research shows that there is wide individual variation in the response to IHE and altitude. This variation exists in both humans and animals, and appears to be due to mechanisms beyond simple iron insufficiency.

2 IHE and Athletic Performance

Expose subjects to 15,000 feet for 1 hour per day over several days for 7 to 11 sessions showed increased blood O2 saturation compared with initial exposure and the benefits were detectable for up to 4 weeks.

Exposure of 30 min to 3 hours every 2 to 3 days for 9 exposures increased hemoglobin by 12% and red blood cells by 22%

Exposure of 3x (6 min low O2, 4 min normal air) per day for 14 days increased breathing volume at altitude by ~50%. Partial pressure of O2 started at 50 mmHg (20,000 ft) dropping to 35 mmHg (28,000 ft). Several studies have shown similar results.

5x (15 min 11% O2 + 15 min recovery) for 14 day produced changes to the metabolic pathways that optimize the use of oxygen.

Other studies in rats indicate that IHE changes the ratio of fat to protein burning in favor of fats by 80%.

Recent studies indicate that IHE stimulates NO (Nitric Oxide) production, with the excess stored in the vascular walls. This improves blood pressure.

Research[2] using highly trained runners showed no running improvement with IHE. However, this study used IHE for 4 weeks and had O2 saturation values of 89.9, 86.3, 85.9, and 81.4 for each week. The value of IHE is dependent upon the O2 saturation levels, with little effect until values under 89%[3]. The athletes in the study therefore only received significant hypoxia for about one week. The athletes were given 5 min hypoxic, 5 min normal for 70 minutes total for five days per week, 4 weeks total.

A similar research[4] study showed a significant improvement in 3K running performance. This study used 90 minutes of IHE (5 hypoxic:5 normal) for 15 days over a three week period, using 13,000 feet at the start to 19,000 feet at the end.

A study[5] looking at Hypoxia EPO, a hormone that stimulates red blood cell production showed a ~50% increase in EPO from 4 hours of IHE or 2 hours of continuous hypoxia, but no response from 5 minutes or 1 hour. The IHE was a simulated altitude of 18,000 ft.

Subjects exposed hypoxia in a hypobaric chamber showed elevated EPO levels after 114 min at 9,000 feet and or after 84 minutes at 12,000 feet. EPO levels continued to rise with longer exposure. [6]

Research using the AltoLab system showed a significant improvement in sprint speed. The study used 6 min hypoxia (10,000 to 18,000 ft) with 4 min recovery for an hour a day for 15 days. The study shown a tiny improvement in blood parameters (hemoglobin/hematocrit) normally associated with altitude training.[7]

A study of elite triathletes showed no changes in blood parameters or running performance after 17 days AltoLab IHE[8]. However, the protocol used has a gradually decreasing O2 level, so that only towards the end of the training is there a significant training stimulus.

3 Intermittent Hypoxic Exposure and Diseases

3.1 Intermittent Hypoxic Exposure and Asthma

Studies have reported an improvement in asthma, with reduced attacks, reduced severity of attacks and reduced need for medication. Note that none of these studies has looked at specifically at exercise induced asthma.

IHE increased lung force in asthmatic and non-asthmatic athletes[10]. There was no deterioration in asthma status from the trial, and half of the asthmatics reported a reduction in the need for medication. The trial used 15 sessions over three weeks, with each session being 5 min hypoxia followed by 5 min normal air, repeated for 60 minutes. The hypoxia was equivalent to 22,500 ft.

IHE has been shown to reduce the shortness of breath and congestion of childhood bronchial asthma, reducing or eliminating the attacks[11]. The protocol was 4 repeats of 5-7 minutes with 12% O2 which resulted in a SpO2 of 89-92%.

Studies have shown IHE reduces the oxidant stress associated with bronchial asthma, however, the study had large variations in individual response[1].

3.2 Neuroprotective Mechanisms of Intermittent Hypoxia

There are a number of studies that show that mild hypoxic exposure provides neural protection against prolonged ischemia[13]. This may provide benefits to those with a high risk of stroke, or other risk of impaired blood flow to the brain.

3.3 Intermittent Hypoxic Exposure and Parkinson's Disease

A study of IHE on adult rats, old rats and old rats that have experimental dopamine deficiency showed an increase in dopamine in the both groups of old rats[14]. The study used 5 repeats of 15 minutes of 12% O2 with 15 minute recoveries for two weeks. While this is an early study, the low risk nature of IHE makes this a promising treatment.

3.4 Intermittent Hypoxic Exposure and Alzheimer's Disease

A study of rats that had induced Alzheimer's Disease through intracerebral injections of beta-amyloid showed that adaptation to IHE may improve the brain's self-defense mechanisms which slow the progression of Alzheimer's. Again, this is an early study on animal, but it shows some promise[15].

3.6 Intermittent Hypoxic Exposure and Oxidative Stress

A study of workers that cleaned up after Chernobyl nuclear reactor explosion showed that they had higher levels of oxidant stress where higher than normal. Exposing the workers to IHE of 3x (5 min 7-8% [28,000+ ft] O2 with 5 min normal air) for 14 days significantly reduced the oxidant stress.

4 Risks of Hypoxic Exposure

There is a case study of an individual who had a seizure after hypoxic exposure[17]. This military officer was undergoing hypoxia training with a Reduced Oxygen Breathing Device. This device is routinely used to protect and prepare for sudden decompression at altitude. The seizure occurred after sleep deprivation (4hr/night for 3 nights) and breathing 7.11% O2, equivalent to 25,000'. Their SpO2 dropped to 69%, which is lower than what is normally considered the safe lower limit of 75%. There is also a study of rats that indicates hypoxia may increase seizure susceptibility[18]. Therefore it seems prudent for individuals with epilepsy to avoid hypoxic training without specific medical approval.

5 A note on terminology

Some literature considers sleeping at altitude (or with low oxygen levels) to be 'IHT'. This Wiki uses IHT to be separate from LHTL and to mean shorter periods than overnight sleep and generally at much lower oxygen concentrations. There is also confusion between the terminology for Intermittent Hypoxic Exposure and Intermittent Hypoxic Training. There is also a use of the term 'Intermittent Normobaric Hypoxic Training', or 'Intermittent Normobaric Hypoxic Treatment' for IHE.